1. Field of the Invention
The present invention relates to a cleaning device for use in an image forming apparatus.
2. Description of the Related Art
Various types of image forming apparatuses, such as electrophotographic types and ink-jet types, are conventionally known. Such image forming apparatuses generally include surface moving members. For example, some electrophotographic image forming apparatuses include surface moving members, such as a latent-image bearing member (an image bearing member), e.g. a photoconductor drum, an intermediate transfer medium (an image bearing member), e.g. an intermediate transfer belt, and a recording material conveyor member, e.g. a paper conveyor belt. Furthermore, some ink-jet image forming apparatuses include surface moving members, such as a recording material conveyor member, e.g. a paper conveyor belt. Generally, unwanted deposit, e.g. toner, may be attached onto a surface of such surface moving member during a use of such image forming apparatuses, thereby causing various problems. Therefore, a cleaning unit that removes the unwanted deposit from the surface of a surface moving member is required. As such cleaning unit, a blade is widely used because preferable performance of removing deposit can be achieved with a simple configuration of the blade. Specifically, such blade removes a deposit by squeezing a cleaning blade made of an elastic material, e.g., polyurethane rubber, onto the surface of a surface moving member.
For a cleaning device having such a blade, two types are known, i.e., a trailing type and a counter type. Respective cleaning devices of the two types are explained below with examples of a cleaning device for a photoconductor in an electrographic image forming apparatus.
FIG. 17A is a schematic diagram for explaining a conventional cleaning device of a trailing type. The conventional cleaning device shown in FIG. 17A includes a photoconductor (surface moving member) 10 and a cleaning blade 231. The photoconductor 10 has a drum shape. The cleaning blade 231 is made of a long elastic material extending along the direction of a photoconductor rotation axis orthogonal to a surface moving direction A of the photoconductor 10. The conventional cleaning device is configured in such a manner that a longitudinally extending edge of the cleaning blade 231 (hereinafter, “contact edge”) is to be pressed on the surface of the photoconductor 10. In the trailing type, the cleaning blade 231 is held with a blade holder (holding member) 232 supported upstream of a normal line N in the photoconductor-surface moving direction by the main body of the cleaning device, where the normal line N is normal to a contact point P on the photoconductor surface in contact with the contact edge of the cleaning blade 231. The trailing type means a configuration in which the holding member holds the elastic member; the supporting unit supports the holding member against the main body of the cleaning device; and the supporting unit is arranged upstream of a normal line in the surface moving direction of the surface moving member, where the normal line is normal to a contact point on the surface of the surface moving member in contact with the contact edge of the elastic member.
FIG. 17B is a schematic diagram for explaining a conventional cleaning device of a counter type. The conventional cleaning device shown in FIG. 17B is configured in such a manner, similar to that shown in FIG. 17A, that the cleaning blade 231 made of a long elastic material extends along the direction of the photoconductor rotation axis orthogonal to the surface moving direction A of the photoconductor 10, and a longitudinally extending contact edge of the cleaning blade 231 is to be pressed on the surface of the photoconductor 10. In the counter type, the cleaning blade 231 is held with the blade holder 232 supported downstream of the normal line N in the photoconductor-surface moving direction by the main body of the cleaning device, the normal line N being normal to the contact point P in contact with the contact edge of the cleaning blade 231. The counter type means a configuration in which the holding member holds the elastic member; the supporting unit supports the holding member against the main body of the cleaning device; and the supporting unit is arranged downstream of the normal line in the surface moving direction of the surface moving member, where the normal line is normal to the contact point on the surface of the surface moving member in contact with the contact edge of the elastic member.
In both, the trailing type and the counter type, if a friction force between the cleaning blade 231 and the photoconductor surface changes due to some reasons while the photoconductor 10 is rotating in operation, flapping (loose movement) of the cleaning blade 231 occurs, consequently causing a problem, such as damage to the photoconductor 10, or abnormal noise. In the trailing type, flapping occurs less often than in the counter type, and even if flapping occurs, it causes few problems. The reason for this is because when the friction force between the cleaning blade 231 and the photoconductor surface increases while the photoconductor 10 is rotating in operation, the cleaning blade 231 of the trailing type can warp towards a direction to release a vertical resistance of the cleaning blade 231; in contrast, the cleaning blade 231 of the counter type cannot warp towards the direction to release the vertical resistance. Moreover, in the counter type, the cleaning blade 231 cannot warp towards the direction to release the vertical resistance, and when the friction force between the cleaning blade 231 and the photoconductor surface increases, a serious problem, i.e., a blade turnup, may occur.
On the other hand, in the counter type, a contact pressure can be increased to be higher than that in the trailing type, so that a removal performance by the counter type is higher than that by the trailing type.
More specifically, in the case of the trailing type, if the cleaning blade 231 is pressed with a large force to increase the contact pressure, the cleaning blade 231 warps, thus causing a redundant touch, in which an upstream side surface 231a of the cleaning blade 231 touches on the photoconductor surface. In this case, the upstream side surface 231a is a surface of the cleaning blade 231 positioned upstream of the contact edge in the photoconductor-surface moving direction. If the redundant touch occurs, a contact area between the cleaning blade 231 and the photoconductor surface suddenly increases. As a result, the contact pressure is inversely decreased despite pressing the cleaning blade 231 with a large force, thus degrading the removal performance. By contrast, in the case of the counter type, even if pressing the cleaning blade 231 with a large force to increase the contact pressure, a friction force works against a warp in the cleaning blade, so that the cleaning blade 231 warps little. Accordingly, a redundant touch less easily occurs even if pressing the cleaning blade 231 with a large force, and a large pressing force can be applied onto a small contact area. Thus, a high contact pressure can be achieved, and a preferable removal performance can be achieved.
Japanese Patent Application Laid-Open No. S60-198574 discloses (see FIG. 8) a cleaning device of the trailing type that cleans a photoconductor. The cleaning device includes a backup member that supports, from the back surface, a force received by the tip of the cleaning blade due to rotation of the photoconductor.
It is appropriately determined whether to use the trailing type or the counter type based on consideration of respective advantages and respective disadvantages. If a high removal performance is required, it is preferable to employ the counter type because of high performance efficiency described above. Specifically, a recent electrophotographic image forming apparatuses often uses a toner of which particles are spherical and have a small diameter, particularly, a polymerized toner, so that an excellent removal performance is required to remove such toner. Thus, a cleaning device of the counter type tends to be employed in many cases, because its removal performance is preferable while the removal performance by a cleaning device of the trailing type is insufficient.
However, the conventional counter type cleaning device has a problem that life durations of the photoconductor and the cleaning blade are shortened, because the cleaning blade is excessively pressed with a large force to increase the contact pressure for obtaining a preferable removal performance. As a result, the photoconductor (surface moving member) to be cleaned and the cleaning blade are excessively worn.
On the other hand, the cleaning device disclosed in the above document No. S60-198574 can achieve a higher contact pressure than that by a general trailing type as shown in FIG. 17A. However, to achieve a contact pressure in the cleaning device as high as that in the counter type, a backup member and a mechanism to support the backup member needs to be reinforced to press down a warp in the cleaning blade. To achieve a similar contact pressure, a simpler configuration and a lower cost can be realized in a cleaning device of the counter type than those in the cleaning device disclosed in the above document No. S60-198574.
Because the counter type can provide a higher contact pressure than the trailing type, the counter type has an advantage of a higher removal performance than the trailing type, and is widely used, as disclosed in Japanese Patent Application Laid-Open No. 2001-312191.
To explain in detail, in the case of the trailing type, if pressing the cleaning blade 231 with a large force to provide a high contact pressure, the cleaning blade 231 warps, and a redundant touch occurs so that the upstream side surface 231a touches on the photoconductor surface. If the redundant touch occurs, a contact area between the cleaning blade 231 and the photoconductor surface suddenly increases. As a result, the contact pressure is inversely decreased despite pressing the cleaning blade 231 with a large force, thus degrading the removal performance. By contrast, in the case of the counter type, even if pressing the cleaning blade 231 with a large force to provide a high contact pressure, a friction force works against a warp in the cleaning blade, so that the cleaning blade 231 warps little. Accordingly, a redundant touch less easily occurs even if pressing the cleaning blade 231 with a large force, and a large pressing force can be applied onto a small contact area. Thus, a high contact pressure can be achieved, and an excellent removal performance can be obtained.
However, when the friction force between the cleaning blade 231 and the photoconductor surface increases while the photoconductor 10 is rotating in operation, the cleaning blade 231 of the trailing type can warp towards a direction to release a vertical resistance of the cleaning blade 231; in contrast, the cleaning blade 231 of the counter type cannot warp towards the direction to release the vertical resistance. Consequently, when the friction force between the cleaning blade 231 and the photoconductor surface increases, a serious problem may occur, e.g., a blade turnup, or an excess load applied on operation of the photoconductor.
Specifically, a recent electrophotographic image forming apparatuses often uses a toner of which particles are spherical and have a small diameter, particularly, a polymerized toner, so that an excellent removal performance is required to remove such toner. Therefore, a sufficient removal performance needs to be ensured, by employing a cleaning device of the counter type, and setting the contact pressure of the cleaning blade as high as possible. Under such situation, a problem easily occurs, such as a blade turnup or an excess load on operation of the photoconductor, because the maximum value of a friction force arising from fluctuation in the friction force between the cleaning blade and the photoconductor surface changes while the photoconductor is rotating in operation.